Three weeks after being vaccinated with FLU-v or placebo, 30 volunteers will be taken to a Quarantine Unit to be exposed to the attenuated H3N2 study virus and then monitored by study physicians and nurses for a 10-11 day period. The other 14 volunteers will be held in reserve as back-ups. If fewer than 30 of the volunteers who travel to the Quarantine Unit are eligible to be exposed to the study virus, then volunteers who have been kept in reserve will be used.